Effects of Flooding on the Sources, Spatiotemporal Characteristics and Human Health Risks of Polycyclic Aromatic Hydrocarbons in Floodplain Soils of the Lower Parts of the River Niger, Nigeria

The concentrations of the 16 US EPA polycyclic aromatic hydrocarbons (PAHs) were determined in the floodplain soils of the lower parts of the River Niger, Nigeria in 2013 and 2014 after recent flood waters had receded completely into the river channels. The aim of the research was to provide data on the spatiotemporal changes in the contamination levels, compositional patterns, sources and human health risks linked with exposure to PAHs in these soils through non-dietary ingestion, inhalation and dermal contact pathways. The PAHs in the soil samples were extracted by ultrasonication with hexane/dichloromethane, followed by clean-up on a silica gel/alumina column, and gas chromatography-mass spectrometry was used for their separation, detection and quantification. The concentrations of the 16 PAHs varied from 812 to 10,700 µg kg−1 in 2013 after an extreme flooding event, and from 12.2 to 2630 µg kg−1 in 2014 after a natural flooding event. The benzo[a]pyrene (BaP) potency factors and incremental life cancer risks (ILCR) were used to evaluate the risks of human exposure to PAHs in these soils. The average total ILCR values obtained for 2014 (a year after the extreme flooding) indicated that there was a probability of 443 children and 308 adults in a population of one million equally exposed individuals at risk of developing cancer or cancer-related illnesses in their lifetime as opposed to 6450 children and 4480 adults in 2013 immediately after the extreme flooding event. This study has shown that flooding events can cause significant variations in pollutant concentrations of floodplain soils that markedly alter human health risks.